Well there's no guarantee that you will or won't tear. The best thing to prevent it is to only push when you feel ready and as the midwife guides you.

I don't think the length has much to do with it as I uderstand it's more to do with being dilated enough for the size of the baby's head. If the midwife thinks you aren't big enough then they will make an incision as this is more controlled and will heal better.

I think tearing is also more common in induced labours as you tend to prgress much quicker.

ranger*goy - have you tried looking on the BabyCentre website? I've tried posting a link for you but for some reason this site won't let me do that! If you go to BabyCentre and do a search for "perineal massage" it will bring up an article which includes info on how to avoid any tears/cuts.